The Cell: An Overview

Chapter 5

5.1 Basic Features of Cell Structure and Function

Cells are small and are visualized using a microscope

Cells have a DNA-containing central region surrounded by cytoplasm

Cells occur in prokaryotic an eukaryotic forms, each with distinctive structures and organization

Microscopes and Cells

Robert Hooke and Anton van Leeuwenhoek

Robert Brown

Mattias Schleiden and Theodore Schwann

Rudolf Virchow

Microscopes and Cells

Fig. 5-1, p. 92

Cell Theory: Fundamental to Life

All organisms are cellular

Cell: the smallest unit of life

Cells come only from preexisting cells

Examples of Cells

Fig. 5-2, p. 92

Units of Measure

Fig. 5-3, p. 93

Research Methods

Fig. 5-4, p. 94

Cells are Small

No life is smaller than an intact cell• Diffusion and surface area to volume ratios

Cells viewed with microscopes• Light and electron

Magnification and resolution limit microscopes

Surface to Volume Ratios

All Cells Contain DNA

All cells have a central region with DNA• Stores hereditary information (connection to

evolution)

• Genes are located on DNA

• Proteins replicate DNA and copy information to RNA

Cytoplasm

Cytoplasm • Surrounds the central region

Cytosol • Aqueous solution of cell

Organelles • Small organized structures within cytosol

Plasma Membrane

Fig. 5-6, p. 95

Plasma Membrane

Plasma membrane defines cytoplasm

Lipid bilayer and proteins

Hydrophobic• Selective passage hydrophilic

Internal environment of cell different from external

Prokaryotes and Eukaryotes

Prokaryotes • No boundary membrane in central region

• Nucleoid

• Domains: Archaea and Bacteria

Eukaryotes • Boundary membrane in central region

• True nucleus

• Domain: Eukarya

Components of Prokaryotic andEukaryotic Cells

Table 5-1, p. 96

5.2 Prokaryotic Cells

Prokaryotic cells have little or no internal membrane structure

Prokaryotic Cell Structure

Fig. 5-7, p. 97

Prokaryotic Internal Structure

Small, little to no membrane structure• Cell wall & capsule

Plasma membrane allows metabolism• ATP in mitochondria and chloroplasts

• Evolution by endosymbiosis

5.3 Eukaryotic Cells

Eukaryotic cells have a membrane-enclosed nucleus and cytoplasmic organelles

Nucleus contains much more DNA than the prokaryotic nucleoid

Cytoplasm has endomembrane systems dividing cell into functional and structural components

5.3 (cont.)

Mitochondria are the powerhouses of the cell

Microbodies carry out vital reactions that link metabolic pathways

The cytoskeleton supports and moves cell structures

Flagella and cilia are the propellers of eukaryotic cells

Eukaryotic Cell Overview

Domain Eukarya (true nucleus) • Includes protists, fungi, plants and animals

Eukaryotic plasma membrane function• Regulate/recognize substances (immune system)

• Cell-to-cell binding

Fungi, plants and many protists have cell walls

Typical Animal Cell

Fig. 5-8a, p. 99

Typical Plant Cell

Fig. 5-9a, p. 100

Eukaryotic Nucleus

Nuclear envelope separates nucleus and cytoplasm• Two membranes and nuclear pores

Nucleoplasm within nuclear envelope• Chromatin and chromosomes

Nucleolus• Genes for ribosomal RNA

Nuclear Envelope

Fig. 5-10, p. 101

Endomembrane System

Endomembrane system • Connects all membranes

• Synthesizes/ modifies membrane proteins

• Synthesizes lipids

• Detoxification

Vesicles exchange membrane throughout endomembrane system• ER, Golgi, nuclear envelope, lysosomes,

vesicles, plasma membrane

Endoplasmic Reticulum

Fig. 5-11, p. 102

Endoplasmic Reticulum

Endoplasmic reticulum (ER) • Interconnected network of membrane with

cisternae and lumen

Rough ER • Ribosomes bound to surface

• Membrane-associated protein synthesis

Endoplasmic Reticulum

Smooth ER • No ribosomes

• Synthesizes lipids and detoxifies

Proportion rough/smooth ER reflect cell activities

Golgi Complex

Fig. 5-12, p. 103

Lysosomes

Lysosomes• Vesicles from Golgi complex

• Hydrolytic enzymes from ER; low pH

Autophagy removes nonfunctional organelles

Phagocytosis digests extracellular material• Major function of immune systems

Endocytosis, Exocytosis and Lysosomes

Fig. 5-13-14, p. 104

Vesicle Traffic

Fig. 5-15, p. 105

Mitochondria

Cellular respiration yields ATP

Mitochondria have two membranes• Outer membrane smooth

• Inner membrane folded (cristae)

• Mitochondrial matrix

Mitochondria have own genome• Endosymbiosis

Mitochondria

Fig. 5-16, p. 106

Microbodies

Microbodies • Single membrane organelles

• Not part of endomembrane system

Microbody enzymes link biochemical pathways

Examples• Peroxisomes, glyoxysomes or glycosomes

Microbodies

Fig. 5-17, p. 107

Cytoskeleton

Cytoskeleton • Maintains shape and organization

• Interconnected protein fibers and tubes

Most prominent in animal cells• Plants and fungi also use cell walls and central

vacuole

Cytoskeleton Examples

Fig. 5-18, p. 107

Cytoskeleton Components

Main elements of animal cytoskeletons• Microtubules are supportive

• Intermediate fibers thinner, interconnected with microtubules

• Microfilaments thinnest

Cytoskeleton Components

Each element assembled from proteins• Microtubules from tubulin

• Intermediate fibers from intermediate filaments

• Microfilaments from actins

Major Components of Cytoskeleton

Fig. 5-19, p. 108

Microtubules

Many microtubules originate from centrosome• Originate from centrioles

• Anchor major organelles

• Microtubules provide tracks for mobile organelles

Microtubules

Organelle movement by motor proteins• Vesicle attached to motor protein “walks” along

microtubule

• Requires ATP

Cytoskeleton allows large cellular movement• Amoeboid motion, cytoplasmic streaming, cell

division

Kinesin

Fig. 5-20a,b, p. 108

Flagella and Cilia

Flagella and cilia for cell motion• Identical structure; cilia shorter/greater in number

Structures are 9+2• Motor proteins

• From centrioles and basal body

Prokaryotes have analogous (not homologous) flagella and cilia

Flagellar Structure

Fig. 5-21, p. 109

Flagellar and Ciliary Beating Patterns

Fig. 5-22, p. 110

Centrioles

Fig. 5-23, p. 110

5.4 Specialized Structures of Plant Cells

Chloroplasts are biochemical factories powered by sunlight

Central vacuoles have diverse roles in storage, structural support, and cell growth

Cell walls support and protect plant cells

Chloroplasts

Chloroplasts have multiple membranes for photosynthesis• Outer smooth, inner folded; stroma inside both

• Thylakoids and grana inside stroma

• Endosymbiosis

Plastids are plant organelles that include chloroplasts, amlyoplasts and chromoplasts

Plastids

Plant organelles including• Chloroplasts

• Amyloplasts

• Chromoplasts

Chloroplast Structure

Fig. 5-24, p. 111

Central Vacuoles

Central vacuoles • Large vesicles in plants

• 90% of many plant cell’s volume

• Turgor pressure from water

• Other functions

Tonoplast • Membrane surrounding central vacuole

Cell Walls

Cell walls • Extracellular structures

• Provide structure and contain pressure

• Cellulose fibers for tensile strength, other organic molecules for compression resistance

Two types of cells walls • Primary

• Secondary

Cell Walls

Middle lamella holds adjacent cell walls together

Plasmodesmata provide cellular connections• No cell wall passage

Cell Wall Structure

Fig. 5-25, p. 112

5.5 The Animal Cell Surface

Cell adhesion molecules organize animal cells into tissues and organs

Cell junctions reinforce cell adhesions and provide avenues of communication

The extracellular matrix organizes the cell exterior

Cell Adhesion and Junctions

Cell adhesion molecules bind cells together nonpermanently• Glycoproteins bind to specific molecules on other

cells

Cell junctions seal spaces between cells permanently• Direct cellular communication

Functions of Cellular Junction

Anchoring junctions “weld” cells together• Desmosomes and adherens

Tight junctions prevent small ion movement • Seal spaces and fuse membranes

Gap junctions allow passage without membrane control • Same tissue

Animal Cell Connections

Fig. 5-26, p. 114

Extracellular Matrix

Collagen proteins • Tensile strength and elasticity

Proteoglycans • Interlinkage

• Changes consistency (jellylike to hard and elastic)

Fibronectins • Connect cells via integrins

Extracellular Matrix

Fig. 5-27, p. 115

Animation: Fluid mosaic model

PLAYANIMATION